I bought a school bus on eBay (site unseen, a 2003 International 3000) and after getting the floor up, I've found that there is very severe rust on the wheel wells and the floor in between. Probably the bottom 2" of the wheel wells themselves are rusted away, and the floor for a couple of inches around the base of the wheel wells is gone as well (so you can see straight down at the tires and the ground).

There are numerous other holes on the floor area between the wheel wells and a couple of feet in front and back of the wells. The transverse channels underneath the floor in this area are severely corroded as well, especially the one to which the mudflaps are attached - these look rather precariously attached now as the bracket is severely corroded along with the channel, although by feel it is still very sturdy and unmoveable (so it doesn't seem as if the mudflaps are about to actually fall off).

If the transverse supporting channels were OK I would feel confident about just patching and/or replacing the sheet metal floor, but they're obviously not OK. Assuming that nothing on the bus chassis is so rusted as to make the bus hopeless (and I don't know this yet, unfortunately), is it possible to remove and rebuild this entire floor section? It seems simple conceptually at least: I would cut the entire section away, then replace the channels with 3" square steel tubing (which I think would give me the correct height) welded to the chair rail on each side and resting on the chassis beams, and then put down a new sheet floor (I'm not sure what guage would be best here for this). I would then bolt the mudflaps (with new brackets) to the tube that replaced the original channel there.

And then my really crazy question: if it's possible (and practical) to rebuild the floor in this way, would it be possible to do the same thing with pressure-treated wood 4x4s and insulate in between with polyiso foam? If this would work, it would give me a well-insulated floor section at the same height as the original bus floor, which as a six-footer would let me stand up straight in this section.

This may all be moot because of other problems, but I'm trying to keep hope alive here.

Go to the UserCP in the upper left and fill out your profile, where are you from, bus info, etc. It'll help us answer your questions. Unless you see considerable rust underneath I would not associate the floor damage with anything exterior. Windows leak and the water concentrates at the wheel wells. Many of us deal with that issue. Most buses have a 3/4" plywood subfloor and a puke mat for total of about 1" of flooring for either 6'3", or high roof model at 6'6", if you frame the floor with 4x4 your losing 3" plus what ever insulation and finish floor you have.

Go to the UserCP in the upper left and fill out your profile, where are you from, bus info, etc. It'll help us answer your questions. Unless you see considerable rust underneath I would not associate the floor damage with anything exterior. Windows leak and the water concentrates at the wheel wells. Many of us deal with that issue. Most buses have a 3/4" plywood subfloor and a puke mat for total of about 1" of flooring for either 6'3", or high roof model at 6'6", if you frame the floor with 4x4 your losing 3" plus what ever insulation and finish floor you have.

I edited my details (sorry, I put "International" for both coach and chassis, I'm not actually sure about the difference).

I'm not talking about putting a 4x4 frame on top of the existing metal sheet floor - I'm talking about replacing the current metal floor (meaning the sheet + the supporting channels on the underside) with a floor made of wooden 4x4s. These 4x4s would be resting directly on top of the chassis beams, so the top of this floor would be at the same height as the original metal sheet floor (which is about 3" - I'm able to measure this height by sticking my tape measure through a big hole in the floor and down to the chassis beam).

I will take some pictures of my wheel well situation tomorrow and post them here (I should have done this to begin with, sorry). But the damage is much worse than in your pictures.

Keep in mind the body is a separate box that just sits on and is bolted to the frame. I'm not sure of the structural rigidity you would retain by removing the floor and replacing it all with wood. Is your bus a Genesis?

Keep in mind the body is a separate box that just sits on and is bolted to the frame. I'm not sure of the structural rigidity you would retain by removing the floor and replacing it all with wood. Is your bus a Genesis?

No, it's an International 3000 (sorry, I'm new at the bus thing and don't really know who made the coach).

It doesn't seem right now that the existing floor channels are providing any structural rigidity because of how corroded they are. I kind of got the impression from looking at the bus underneath that there are much stronger channels every 8 feet or so (equally distant from the front and back of the wells) and that these are supporting the chair rails and hence the walls and roof, but the smaller channels in between are more just stiffeners for the floor sheet. I'm definitely not sure of this, but if those channels are significant weight-bearers I'm in trouble given their condition (although I think you were referring to the stiffness and not necessarily the load bearing).

Keep in mind the body is a separate box that just sits on and is bolted to the frame. I'm not sure of the structural rigidity you would retain by removing the floor and replacing it all with wood. Is your bus a Genesis?

Also I'm not suggesting replacing the entire floor this way, just maybe an 8-foot section around the wheel wells.

The NY title has year 2003, make/model "AM/TR". I feel like I should know what the hell my own bus is but I don't. When I went to do the title transfer the DMV person asked me what "AM/TR" meant and I had to go find out before they would do the transfer.

I thought an FE has the engine in front but also a flat front? I think mine is a CE (I don't know what that stands for) - is my bus actually a CE 300?